HTTP Protocol

HyperText Transfer Protocol(超文本传送协议)

client/server model

transport protocol - TCP
HTTP 1.0 - RFC 1945
HTTP 1.1 - RFC 2068
Port - 80

HTTP 1.0	HTTP 1.1
a TCP tranmit one object	TCP transmit multiple objects

server maintains no information about past client requests

Non-persistent
- HTTP/1.0
- server parses requests, responses, and close TCP connections
- 2 RTTs(Round Trip Time) to fetch each object
- slow start for each object transfer
Persistent
default for HTTP/1.1
on same TCP connection(see as above)
client sends requests for all referenced objects as soon as it receives base HTML
Fewer RTTs
Less slow start

Request

request line

method URL version

method

method	introduction	usage
GET	Requests a representation of the specified resource	only retrieves data
HEAD	Asks for a response identical to a GET request, but without the response body	often retrieves the meta information of resource
POST	Submits an entity to the specified resource	often causes a change in state or side effects on the server
PUT	Replaces all current representations of the target resource with the request payload	often updates the resource that existed or provides new resource
DELETE	Deletes the specified resource	deletes resource
CONNECT	Establishes a tunnel to the server identified by the target resource	often for proxy servers
OPTIONS	Describes the communication options for the target resource	requests for available options
TRACE	Performs a message loop-back test along the path to the target resource	often for tests and diagnoses
PATCH	Applies partial modifications to a resource	often for tests and diagnoses

header lines(multiple lines formatted the same as below)

header field name:value
header field name:value
...

header field name

header field name	introduction
Accept	Informs the server about the types of data that can be sent back
Accept-Encoding	The encoding algorithm, usually a compression algorithm, that can be used on the resource sent back
Accept-Language	Informs the server about the human language the server is expected to send back
Connection	Controls whether the network connection stays open after the current transaction finishes
Host	Specifies the domain name of the server (for virtual hosting), and (optionally) the TCP port number on which the server is listening
Referer	The address of the previous web page from which a link to the currently requested page was followed
User-Agent	Contains a characteristic string that allows the network protocol peers to identify the application type, operating system, software vendor or software version of the requesting software user agent
Cookie	Contains stored HTTP cookies previously sent by the server with the Set-Cookie header
Cache-Control	Directives for caching mechanisms in both requests and responses

Response

status line

version status_code status_description

status codes

header lines(multiple lines formatted the same as below)

header field name:value
header field name:value
...

header field name

header field name	introduction
Date	Contains the date and time at which the message was originated
Content-Type	Indicates the media type of the resource
Content-Length	The size of the resource, in decimal number of bytes
Content-Encoding	Used to specify the compression algorithm
Last-Modified	The last modification date of the resource, used to compare several versions of the same resource
Set-Cookie	Send cookies from the server to the user-agent

satisfy client request without involving origin server

web accesses via web cache
client sends all http requests to web cache
- If objects at web cache, web cache immediately returns the objects in http response
- Else requests objects from the origin server, then returns http response to client
Advantages
- smaller response time
- decrease traffic to distant servers